1. Technical Field of the Invention
The present invention relates to a sliding member, for instance a piston ring or a valve driving member such as roller tappet shaft for internal combustion engines, or a vane for rotary compressors, covered with a physical vapor deposition film of CrN.
2. Description of the Related Art
The technology of the conventional art is disclosed as related below, for improvement of a physical vapor deposition film of CrN for covering the surfaces of a sliding member.
1. Japanese Patent Laid-Open No. 6-248425
A film with a thickness of 1 to 80 micrometers and comprised of CrN having a porosity of 1.5 to 20 percent is formed on the outer circumferential surface of the piston ring, thereby peeling in the film caused by pitting fatigue is suppressed. The film is characterized in having; a columnar crystal structure formed in the direction of the film thickness, a preferred orientation (111) parallel to the outer circumferential surface, a film formed by an ion plating method, and a Vicker's hardness of 600 to 1000.
The preferred orientation (111) is also described as an important factor in Japanese Patent Laid-Open No. 6-293954.
2. Japanese Patent Laid-Open No. 6-265023
Toughness and scuffing resistance of the film can be improved by containing oxygen in 3 to 20 percent by weight in a solid solution state in a crystal structure of CrN. The film has a Vicker's hardness of 1600 to 2200.
In the aforementioned technology of the conventional art, there is no mention of superior resistance to cracks in the physical vapor deposition film of CrN with a preferred orientation (200) parallel to the surface being covered; and there is absolutely nothing to suggest that a film having the specified porosity and preferred orientation (200) has superior resistance to cracks.